As is known in the art of telephony, a host telephone typically has coupled thereto a telephone handset. The host telephone typically includes either a carbon microphone or an electret microphone.
As is also known, there has been a trend to provide host telephones having coupled thereto both a telephone handset and a telephone headset. Such telephone headsets are typically used in those applications in which it is desirable to provide a user having so-called "hands free" telephone operation.
Each of the different microphone types have different electrical characteristics including different impedance characteristics. To efficiently couple signals from the microphone to the headset, the headset amplifier should present a suitable impedance to the particular microphone. Thus, different headset amplifiers each having preselected electrical characteristics are often used to couple a particular type of microphone to the headset.
As is also known, the power requirements for each of the different microphones are different. For example, carbon microphones require a relatively high amount of power. Thus, such power may be coupled directly from the telephone line to which the microphone is connected.
Dynamic and electret microphones, however, typically require less power than can be coupled from the telephone line without sacrificing overall system performance. Thus, those systems which employ dynamic and electret microphones, are generally adapted to operate from power provided by an alternating current (AC) source or in those cases in which AC power is unavailable or inconvenient, a battery may be used.
When a battery is employed it is desirable to conserve the battery power. The headset amplifier may sometimes remain powered longer than needed, and consequently drain the battery. Thus, it would be desirable to provide a headset amplifier which may operate on battery power but which conserves battery power when the headset amplifier is not receiving signals from the host telephone or a telephone headset.